diff --git a/client/src/client/workers/test-evaluator.js b/client/src/client/workers/test-evaluator.js
index c13b3c3b79..78d309cf41 100644
--- a/client/src/client/workers/test-evaluator.js
+++ b/client/src/client/workers/test-evaluator.js
@@ -38,7 +38,7 @@ const __utils = (() => {
     self.postMessage(data);
   }
 
-  function logToBoth(err) {
+  function log(err) {
     if (!(err instanceof chai.AssertionError)) {
       // report to both the browser and the fcc consoles, discarding the
       // stack trace via toString as it only useful to debug the site, not a
@@ -47,14 +47,14 @@ const __utils = (() => {
     }
   }
 
-  const toggleLogging = on => {
-    self.console.log = on ? proxyLog : () => {};
+  const toggleProxyLogger = on => {
+    self.console.log = on ? proxyLog : oldLog;
   };
 
   return {
     postResult,
-    logToBoth,
-    toggleLogging
+    log,
+    toggleProxyLogger
   };
 })();
 
@@ -66,7 +66,8 @@ self.onmessage = async e => {
   // Fake Deep Equal dependency
   const DeepEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);
 
-  __utils.toggleLogging(e.data.firstTest);
+  // User code errors should be reported, but only once:
+  __utils.toggleProxyLogger(e.data.firstTest);
   /* eslint-enable no-unused-vars */
   try {
     let testResult;
@@ -84,7 +85,7 @@ self.onmessage = async e => {
         throw err;
       }
       // log build errors
-      __utils.logToBoth(err);
+      __utils.log(err);
       // the tests may not require working code, so they are evaluated even if
       // the user code does not get executed.
       testResult = eval(e.data.testString);
@@ -97,10 +98,11 @@ self.onmessage = async e => {
       pass: true
     });
   } catch (err) {
-    // report errors that happened during testing, so the user learns of
-    // execution errors and not just build errors.
-    __utils.toggleLogging(true);
-    __utils.logToBoth(err);
+    // Errors from testing go to the browser console only.
+    __utils.toggleProxyLogger(false);
+    // Report execution errors in case user code has errors that are only
+    // uncovered during testing.
+    __utils.log(err);
     // postResult flushes the logs and must be called after logging is finished.
     __utils.postResult({
       err: {
diff --git a/client/src/templates/Challenges/redux/execute-challenge-saga.js b/client/src/templates/Challenges/redux/execute-challenge-saga.js
index 3ab11d8a6c..477cf0dbf5 100644
--- a/client/src/templates/Challenges/redux/execute-challenge-saga.js
+++ b/client/src/templates/Challenges/redux/execute-challenge-saga.js
@@ -26,6 +26,7 @@ import {
 
 import {
   buildChallenge,
+  canBuildChallenge,
   getTestRunner,
   challengeHasPreview,
   updatePreview,
@@ -153,15 +154,17 @@ function* previewChallengeSaga() {
     yield fork(takeEveryConsole, logProxy);
 
     const challengeData = yield select(challengeDataSelector);
-    const buildData = yield buildChallengeData(challengeData);
-    // evaluate the user code in the preview frame or in the worker
-    if (challengeHasPreview(challengeData)) {
-      const document = yield getContext('document');
-      yield call(updatePreview, buildData, document, proxyLogger);
-    } else if (isJavaScriptChallenge(challengeData)) {
-      const runUserCode = getTestRunner(buildData, { proxyLogger });
-      // without a testString the testRunner just evaluates the user's code
-      yield call(runUserCode, null, 5000);
+    if (canBuildChallenge(challengeData)) {
+      const buildData = yield buildChallengeData(challengeData);
+      // evaluate the user code in the preview frame or in the worker
+      if (challengeHasPreview(challengeData)) {
+        const document = yield getContext('document');
+        yield call(updatePreview, buildData, document, proxyLogger);
+      } else if (isJavaScriptChallenge(challengeData)) {
+        const runUserCode = getTestRunner(buildData, { proxyLogger });
+        // without a testString the testRunner just evaluates the user's code
+        yield call(runUserCode, null, 5000);
+      }
     }
   } catch (err) {
     console.log(err);
diff --git a/client/src/templates/Challenges/utils/build.js b/client/src/templates/Challenges/utils/build.js
index cc2529c18f..e38188c7e5 100644
--- a/client/src/templates/Challenges/utils/build.js
+++ b/client/src/templates/Challenges/utils/build.js
@@ -71,6 +71,11 @@ const buildFunctions = {
   [challengeTypes.backEndProject]: buildBackendChallenge
 };
 
+export function canBuildChallenge(challengeData) {
+  const { challengeType } = challengeData;
+  return buildFunctions.hasOwnProperty(challengeType);
+}
+
 export async function buildChallenge(challengeData) {
   const { challengeType } = challengeData;
   let build = buildFunctions[challengeType];
diff --git a/client/src/templates/Challenges/utils/frame.js b/client/src/templates/Challenges/utils/frame.js
index 5badae5165..cf1cd9b040 100644
--- a/client/src/templates/Challenges/utils/frame.js
+++ b/client/src/templates/Challenges/utils/frame.js
@@ -104,8 +104,8 @@ const initTestFrame = frameReady => ctx => {
 const initMainFrame = (frameReady, proxyLogger) => ctx => {
   waitForFrame(ctx).then(() => {
     // Overwriting the onerror added by createHeader to catch any errors thrown
-    // after the frame is ready. It has to be overwritten, as proxyUpdateConsole
-    // cannot be added as part of createHeader.
+    // after the frame is ready. It has to be overwritten, as proxyLogger cannot
+    // be added as part of createHeader.
     ctx.window.onerror = function(msg) {
       console.log(msg);
       if (proxyLogger) {